Semiconductor device and method of manufacturing the same

ABSTRACT

To obtain a semiconductor device and a method of manufacturing the same which can reduce influence of fluctuation in characteristic among transistors due to fluctuation in laser light irradiation number and laser light intensity on a semiconductor. There is provided a semiconductor device with plural pixels having transistors forming a matrix pattern, in which: the transistors have semiconductors crystallized by laser light irradiation; the semiconductors stretch over at least two pixels; the length of each of the semiconductors is longer than the pixel pitch of the pixels; and when the scan pitch of the laser light is given as M and the pixel pitch of the pixels is given as N, the semiconductors are irradiated with the laser light N/M times or more.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a semiconductor device and amethod of manufacturing the same. Specifically, the present inventionrelates to a semiconductor device in which a transistor is formed from apolycrystalline semiconductor crystallized by laser light irradiationand to a method of manufacturing the semiconductor device. The inventionalso relates to a semiconductor device which uses the above transistorin its pixel and to a method of manufacturing the semiconductor device.

[0003] 2. Description of the Related Art

[0004] In recent years, portable equipment such as PDAs, cellularphones, and notebook computers have grown popular. Such equipment hasflat panel displays mounted thereto. Flat panel displays employed oftenare STN liquid crystal displays, amorphous silicon TFT (amorphoussilicon thin film transistor) liquid crystal displays, and the like.However, lately these displays have been taken over by low temperaturepolysilicon (polycrystalline silicon) TFT liquid crystal displays inwhich driving circuits are built on glass substrates. In near future,even they will be replaced by light emitting displays (e.g., ELdisplays) that use low temperature polysilicon TFTs as major flat paneldisplays mounted to portable equipment.

[0005] An example of a pixel circuit in a light emitting display isshown in FIG. 26, and the operation thereof will be described briefly.The pixel circuit shown in FIG. 26 controls a current flowing into alight emitting element 2602 (hereinafter referred to as light emissioncurrent) by controlling Vgs (gate-source voltage) of a drivingtransistor 2601. The value of the light emission current and theluminance of the light emitting element are in proportion to each other.Therefore, the luminance of the light emitting element can be controlledby controlling the light emission current.

[0006] Light emitting elements can be formed of a wide range ofmaterials including organic materials, inorganic materials, and bulkmaterials. Among them, a typical light emitting element is an organiclight emitting diode (OLED), which is mainly composed of organicmaterials. A light emitting element is structured to have an anode, acathode, and a light emitting layer which is sandwiched between theanode and the cathode. A light emitting layer is formed of one or morematerials chosen from the above materials. Luminescence provided bylight emitting layers is divided into light emission upon return to thebase state from singlet excitation (fluorescence) and light emissionupon return to the base state from triplet excitation (phosphorescence).The present invention is applicable to a case in which one of the twotypes of light emission is used as well as a case in which both types oflight emission is used.

[0007]FIG. 27A is a circuit diagram of a circuit composed of the lightemitting element 2602 and the driving transistor 2601. FIG. 27B showsthe relation between Vgs (gate-source voltage) of the driving transistor2601 and the light emission current. In FIG. 27B, there are two curvesindicating that the characteristic of one driving transistor 2601 isdifferent from the characteristic of another driving transistor 2601.When the driving transistor 2601 is fluctuated in characteristic asshown in FIG. 27B, the light emission current is also fluctuated eventhough Vgs stays the same level. Accordingly, fluctuation incharacteristic of the driving transistor 2601 has to be avoided in orderto display an image in accurate gray scales. It is impossible to displayan image in correct gray scales if mobility, threshold, and othercharacteristics of the driving transistor 2601 are fluctuated.

[0008] On the other hand, low temperature polysilicon TFTs aredistinctively high-performance TFTs formed on glass substrates. In orderto enhance the performance of a TFT, the crystallinity of asemiconductor (specifically a channel formation region) in thetransistor has to be improved.

[0009] A widely used method for improving the crystallinity of asemiconductor is to irradiate an amorphous state semiconductor withlaser light and crystallize the semiconductor (polycrystallization ormaking amorphous silicon into polysilicon). According to this method,only a portion irradiated with laser light receives high energy andtherefore unnecessarily subjecting the entire substrate to hightemperature can be avoided. A TFT formed by this method is called a lowtemperature polysilicon TFT.

[0010] A TFT formed by a method in which a semiconductor layer iscrystallized by thermal annealing is called a high temperaturepolysilicon TFT.

[0011] In many cases, a laser used in forming a low temperaturepolysilicon TFT is an excimer laser and its laser light is shaped into alinear shape before irradiating a glass substrate. The entire glasssubstrate is irradiated with the laser light by running the linear laserlight over the substrate.

[0012]FIG. 28 is a schematic diagram of laser light irradiation. Alinear laser 2801 is scanned (irradiated) in Direction x. In FIG. 28,the linear laser irradiates parallel to the source driver and scanningby the laser is moved in parallel to the gate driver. Such laser lightirradiation method is described in, for example, JP 2756530 B.

[0013] The description given next is about how pixels are arranged intoa matrix pattern in a pixel portion. In a pixel region 2802 of FIG. 28,plural pixels are arranged to form a matrix pattern. If the pixelportion is for displaying a monochrome image, the pixels are placed atregular intervals in the longitudinal direction and the lateraldirection both. On the other hand, if the pixel portion is fordisplaying a color image, there are various ways to arrange R pixels, Gpixels, and B pixels.

[0014] Methods of arranging pixels for R color, pixels for G color, andpixels for B color are described with reference to FIGS. 29A and 29B.FIG. 29A shows a longitudinal stripe arrangement in which pixels for thesame color are lined up longitudinally. FIG. 29B shows a deltaarrangement in which pixels on one row and pixels on the next row arestaggered by half a sub-pixel.

[0015] In the longitudinal stripe arrangement, the length of a stripe ofR color pixels in the lateral direction is one third the length of thisstripe in the longitudinal direction. The same applies to a stripe of Gcolor pixels and a stripe of B color pixels. If an R color pixel, a Gcolor pixel, and a B color pixel together make one pixel, the length ofthis pixel in the longitudinal direction is equal to the length of thepixel in the lateral direction to form a square shape. In other words, apixel pitch N of one pixel in the longitudinal direction is equal to apixel pitch N of the one pixel in the lateral direction. In the deltaarrangement, the length of an R color pixel (sub-pixel) in thelongitudinal direction is the same as its length in the lateraldirection. The same applies to a G color pixel (sub-pixel) and a B colorpixel (sub-pixel). In other words, an R color pixel (sub-pixel), a Gcolor pixel (sub-pixel), and a B color pixel (sub-pixel) each have asquare shape.

[0016] As has been described, a semiconductor crystallized by linearlaser light irradiation is used in a low temperature polysilicon TFT.Here, referring to the laser light intensity distribution (FIG. 30), adescription is given on the operation of a linear laser when asemiconductor is irradiated with laser light by running the linear laserover the semiconductor.

[0017] First, one point in a semiconductor is irradiated with a linearlaser. The laser light intensity distribution at this stage often formsa hill shape as shown in FIG. 30. An example thereof is Gaussiandistribution. Thereafter, the laser light irradiation position is movedin Direction x by a laser scan pitch M to irradiate the semiconductorwith the linear laser again. Then the laser light irradiation positionis once more moved in Direction x to proceed laser light irradiation.The same operation is repeated to irradiate the entire glass substratewith the laser.

[0018] In this laser light irradiation, some regions of thesemiconductor are irradiated with the laser light many times whereassome other regions are irradiated with the laser light only a few timesdepending on where they are located in Direction x (the laser scanningdirection) as shown in FIG. 30. In short, the laser light irradiationnumber varies from one region of the semiconductor to another.

[0019] Furthermore, the intensity of laser light emitted from a laser isnot constant but is fluctuated. This means that regions of asemiconductor cannot be irradiated uniformly with laser light even ifthey receive the same number of laser light irradiation.

[0020] When the number of laser light irradiation and the laser lightintensity are varied from one region of a semiconductor to another, thecrystallinity of the semiconductor crystallized by the laser is alsofluctuated. Transistors formed from a semiconductor that has unevencrystal state are fluctuated in characteristic.

[0021] If transistors that are fluctuated in characteristic are used tomanufacture a light emitting display, the driving transistor 2601 of onepixel and the driving transistor 2601 of another pixel exhibit differentcharacteristics. Such light emitting display is incapable of displayingan image in accurate gray scales.

[0022]FIG. 31 shows the light emitting display which is displaying anuneven image because of the influence of fluctuation in characteristicof the driving transistor 2601. This uneven image is due to varyinglaser light irradiation number and laser light intensity, which differfrom one point to another in Direction x (the laser scanning direction)of the semiconductor. As a result, streaks parallel to Direction yappear showing laser light irradiation tracks. This type of imageunevenness is hereinafter referred to as laser fringes.

SUMMARY OF THE INVENTION

[0023] The present invention has been made in view of the above, and anobject of the present invention is therefore to provide a semiconductordevice free of the above problems and a method of manufacturing thesemiconductor device. Specifically, an object of the present inventionis to provide a semiconductor device and a method of manufacturing thesame which can reduce influence of fluctuation in characteristic amongtransistors due to fluctuation in laser light irradiation number andlaser light intensity on a semiconductor. Another object of the presentinvention is to provide a semiconductor device with less laser fringesand a method of manufacturing the semiconductor device.

[0024] In order to solve the above problems, according to the presentinvention, there is provided a semiconductor device with plural pixelshaving transistors forming a matrix pattern, characterized in that:

[0025] the transistors have semiconductors crystallized by laser lightirradiation; and

[0026] each channel formation region of the transistors is placed so asto be parallel to the laser scanning direction.

[0027] According to the present invention, there is provided asemiconductor device with plural pixels having transistors, the pixelsand the wires forming a matrix pattern, characterized in that:

[0028] the transistors have semiconductors crystallized by laser lightirradiation; and

[0029] each channel formation region of the transistors is placed so asto be parallel to the laser scanning direction and to stretch over aregion longer than the pixel pitch.

[0030] According to the present invention, there is provided asemiconductor device with plural transistors forming a matrix pattern,characterized in that:

[0031] the transistors have semiconductors crystallized by laser lightirradiation;

[0032] each channel formation region of the plural transistors is placedso as to stretch in a first direction;

[0033] of the plural transistors, at least two transistors adjacent toeach other in a second direction that is perpendicular to the firstdirection have a positional relation that makes them staggered in thesecond direction; and

[0034] of the semiconductors of the plural transistors, at least twosemiconductors adjacent to each other in the second direction have thesame crystal state.

[0035] According to the present invention, there is provided asemiconductor device with plural pixels having transistors forming amatrix pattern, characterized in that:

[0036] the transistors have semiconductors crystallized by laser lightirradiation;

[0037] the semiconductors stretch over at least two pixels;

[0038] the length of each of the semiconductors is longer than the pixelpitch of the pixels; and

[0039] when the scan pitch of the laser light is given as M and thepixel pitch of the pixels is given as N, the semiconductors areirradiated with the laser light N/M times or more.

[0040] According to the present invention, there is provided a method ofmanufacturing a semiconductor device, including:

[0041] irradiating semiconductors with laser light for crystallization;and

[0042] forming transistors from the crystallized semiconductors andarranging the transistors into a matrix pattern,

[0043] the method being characterized in that:

[0044] each channel formation region of the plural transistors is placedso as to stretch in a first direction;

[0045] of the plural transistors, at least two transistors adjacent toeach other in a second direction that is perpendicular to the firstdirection have a positional relation that makes them staggered in thesecond direction; and

[0046] of the semiconductors of the plural transistors, at least twosemiconductors adjacent to each other in the second direction have thesame crystal state.

[0047] According to the present invention, there is provided a method ofmanufacturing a semiconductor device, including:

[0048] irradiating semiconductors with laser light for crystallization;

[0049] forming transistors from the crystallized semiconductors; and

[0050] forming pixels from the transistors and arranging the pixels intoa matrix pattern,

[0051] the method being characterized in that:

[0052] the semiconductors stretch over at least two pixels;

[0053] the length of each of the semiconductors is longer than the pixelpitch of the pixels; and

[0054] when the scan pitch of the laser light is given as M and thepixel pitch of the pixels is given as N, the semiconductors areirradiated with the laser light N/M times or more.

[0055] In the present invention, semiconductors are placed in parallelto Direction x (the laser light scanning direction) to even outfluctuation in characteristic between a transistor in one point inDirection x (the laser light scanning direction) and a transistor inanother point. By arranging transistors in parallel to Direction x (thelaser light scanning direction), channel formation regions of thetransistors are irradiated with a laser in an increased number of times.This reduces fluctuation in laser light irradiation number andaccordingly reduces fluctuation in crystal state between thesemiconductors. Influence of fluctuation in characteristic among thetransistors having the above semiconductors thus can be lowered.

[0056] Furthermore, in the present invention, each semiconductor isarranged so as to stretch over at least two pixels in order to increasethe number of times the semiconductor is irradiated with the laser. Thismakes the length of the semiconductor larger than the pixel pitch of thepixels. By thus increasing the transistor size and, for example, settinga channel length L larger than the channel width, fluctuation intransistor itself can be reduced.

[0057] The width and length of laser light and the laser scan pitch inirradiating the semiconductors are not particularly limited. However,since the semiconductors are irradiated with a laser an increased numberof times in the present invention, widening the laser light and measuresto the similar effect are preferable. This makes it possible to furtherreduce fluctuation in crystal state between the semiconductors. If eachsemiconductor is sufficiently long, the laser light irradiation numberfor each semiconductor can be satisfactorily large and fluctuation amongtransistors is reduced even when the laser scan pitch is somewhatlarger. In this way, a semiconductor device is manufactured withoutincreasing the total number of laser light irradiation for irradiatingthe entire pixel portion. As a result, processing speed in manufactureof a semiconductor device is raised and therefore the cost is lowered.

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In the accompanying drawings:

[0059]FIG. 1 is a schematic diagram showing arrangement of transistorsof the present invention;

[0060]FIG. 2 is a diagram showing layout of circuits of the presentinvention;

[0061]FIG. 3 is a circuit diagram for circuits of the present invention;

[0062]FIGS. 4A and 4B are a top view of circuits of the presentinvention and a sectional view thereof;

[0063]FIG. 5 is a schematic diagram showing arrangement of transistorsof the present invention;

[0064]FIG. 6 is a diagram showing layout of circuits of the presentinvention;

[0065]FIG. 7 is a schematic diagram showing arrangement of transistorsof the present invention;

[0066]FIG. 8 is a diagram showing layout of circuits of the presentinvention;

[0067]FIG. 9 is a circuit diagram for circuits of the present invention;

[0068]FIGS. 10A and 10B are a top view of circuits of the presentinvention and a sectional view thereof;

[0069]FIG. 11 is a schematic diagram showing arrangement of transistorsof the present invention;

[0070]FIG. 12 is a schematic diagram showing arrangement of transistorsof the present invention;

[0071]FIG. 13 is a diagram showing layout of circuits of the presentinvention;

[0072]FIG. 14 is a circuit diagram for circuits of the presentinvention;

[0073]FIGS. 15A and 15B are a top view of circuits of the presentinvention and a sectional view thereof;

[0074]FIG. 16 is a schematic diagram showing arrangement of transistorsof the present invention;

[0075]FIG. 17 is a diagram showing layout of circuits of the presentinvention;

[0076]FIG. 18 is a circuit diagram for circuits of the presentinvention;

[0077]FIG. 19 is a schematic diagram showing arrangement of transistorsof the present invention;

[0078]FIG. 20 is a diagram showing layout of circuits of the presentinvention;

[0079]FIG. 21 is a circuit diagram for circuits of the presentinvention;

[0080]FIG. 22 is a schematic diagram showing arrangement of transistorsof the present invention;

[0081]FIG. 23 is a sectional view of a semiconductor device of thepresent invention;

[0082]FIG. 24 is a sectional view of a semiconductor device of thepresent invention;

[0083]FIGS. 25A to 25H are diagrams of electronic equipment using asemiconductor device of the present invention;

[0084]FIG. 26 is a circuit diagram of a conventional pixel;

[0085]FIGS. 27A and 27B are diagrams showing the operation of aconventional pixel;

[0086]FIG. 28 is a schematic diagram showing conventional laser lightirradiation;

[0087]FIGS. 29A and 29B are diagrams showing conventional arrangement ofpixels;

[0088]FIG. 30 is an intensity distribution diagram of conventional laserlight;

[0089]FIG. 31 is a diagram illustrating a display screen of aconventional semiconductor device;

[0090]FIG. 32 is a schematic diagram showing arrangement of transistorsof prior art;

[0091]FIGS. 33A and 33B are diagrams showing arrangement of pixels ofprior art;

[0092]FIGS. 34A and 34B are diagrams showing arrangement of pixels ofprior art; and

[0093]FIGS. 35A and 35B are a top view of circuits of the presentinvention and a sectional view thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0094] [Embodiment Mode 1]

[0095] An embodiment mode of a semiconductor device according to thepresent invention will be described with reference to FIGS. 1 to 6. FIG.1 is a schematic diagram of arrangement of transistors in pixels. FIG. 1shows three pixels for red, green, and blue arranged in accordance withthe stripe arrangement. However, the number of pixels in FIG. 1 will benine if one pixel is to have one color. For discrimination, the R colorportion of the first pixel from the top of FIG. 1 is referred to aspixel R(i−1), the G color portion thereof is pixel G(i−1), and the Bcolor portion thereof is pixel B(i−1). Similarly, the R color portion ofthe second pixel from the top is referred to as pixel R(i), the G colorportion thereof is G(i), and the B color portion thereof is pixel B(i).The R color portion of the third pixel from the top is referred to aspixel R(i+1), the G color portion thereof is G(i+1), and the B colorportion thereof is pixel B(i+1).

[0096] Each pixel has transistors. For instance, the pixel R(i−1) has atransistor for driving a light emitting element of the pixel. Thistransistor is called a pixel R(i−1) driving transistor 101. Similarly,the pixel R(i) has a pixel R(i) driving transistor 102, and the pixelR(i+1) has a pixel R(i+1) driving transistor 103. The same applies tothe rest of the pixels.

[0097] In this embodiment mode, a driving transistor of each pixel isextended to a region of a surrounding pixel as shown in FIG. 1. To bespecific, the pixel R(i+1) driving transistor 103 is extended to aregion of the pixel R(i). Similarly, the pixel R(i) driving transistor102 is extended to a region of the pixel R(i−1). Thus a drivingtransistor of one pixel is placed not only on the one pixel but also ona region of a surrounding pixel.

[0098] The length of a driving transistor can therefore be set largerthan the pixel pitch. Thus, the laser scanning direction and a directionin which the channel formation region of a transistor stretches can bemade parallel to each other, whereby the number of times each drivingtransistor is irradiated with laser light is increased. Thereforefluctuation in characteristic among transistors is reduced.

[0099] Here, as shown in FIG. 30, the laser scan pitch is given as M,and the pixel pitch as N. As shown in FIG. 1, the transistor length 104is given as Z. Then one transistor is irradiated with laser light Z/Mtimes. Since Z>N, Z/M is larger than N/M (Z/M>N/M).

[0100] According to the present invention, the number of times atransistor is irradiated with laser light is thus increased andtherefore fluctuation in characteristic among transistors can bereduced. Further, if the transistor length Z is sufficiently long, thelaser scan pitch M can be set slightly larger than that in prior art.This makes it possible to reduce the laser light irradiation number forirradiating the entire pixel portion. However, in FIG. 1, the transistorlength Z starts in one pixel and ends in an adjacent pixel, meaning thatthe scan pitch M is preferably set twice or less in order to increasethe number of times the transistor is irradiated. As a result,processing speed in manufacture of a semiconductor device is raised andmanufacture cost is accordingly lowered.

[0101]FIG. 2 is a layout diagram for the pixel in FIG. 1. The pixel R(i)alone is shown as an example in FIG. 2. A circuit diagram for FIG. 2 isFIG. 3. A sectional view of FIG. 2 is FIG. 4B. FIGS. 2 to 4B use thesame symbols for identical components.

[0102] Features of the layout diagram shown in FIG. 2 are as follows.

[0103] The first feature is that a driving transistor of one pixel isextended to a region of another pixel and therefore the layer of asource wire is used as a selecting gate line. This makes the selectinggate line intersect and overlap the driving transistor. As a result,driving transistor layout is simplified.

[0104] For example, in FIG. 2, an (i−1)-th row selecting gate line 203is arranged to overlap the pixel R(i) driving transistor 102.Accordingly, it is easy to place the driving transistor so as to reach aregion of another pixel.

[0105] A power supplying line intersects and overlaps a selecting gateline, and the overlapped portion can be formed from the layer of a gatewire. For example, a j-th column power supplying line 205 is arranged tointersect and overlap the (i−1)-th row selecting gate line 203. At theintersection, the j-th column power supplying line 205 is formed of thelayer of a gate wire. Thus a power supplying line can overlap aselecting gate line.

[0106] Only a portion of a power supplying line that intersects aselecting gate line is formed from the layer of a gate wire. However, aslong as a power supplying line is allowed to intersect a selecting gateline, the intersection in the power supplying line can be formed of anywire layer.

[0107] Another feature is that a driving transistor is arranged inparallel to a power supplying line and a source signal line. Forexample, the pixel R(i) driving transistor 102 is in parallel to thepower supplying line and the source signal line. Therefore a longtransistor can be placed efficiently in each pixel.

[0108] By setting the positional relation between a selecting gate lineand a power supplying line in this way, a driving transistor can have alength larger than the pixel pitch. To be specific, the length of achannel formation region of a driving transistor can be set larger thanthe pixel pitch.

[0109] The driving transistors shown in FIG. 2 have long channelformation regions: a long channel formation region 201 and a longchannel formation region 202. The long channel formation region 201 andthe long channel formation region 202 together make the longest channelformation region of a driving transistor. The length of this channelformation region which is the sum of the lengths of two channelformation regions is longer than the pixel pitch, about twice the pixelpitch. Therefore each transistor is irradiated with laser light anincreased number of times and fluctuation in characteristic amongtransistors is reduced.

[0110] Lastly, novel points in the layout diagram of FIG. 2 will bedescribed. The features reside in arrangement of driving transistors. InFIG. 2, the pixel R(i) driving transistor 102 is extended to a region ofthe pixel R(i−1) but not the pixel R (i+1). This is for dealing withnoises from the selecting gate line. To elaborate, noises from aselecting gate line, which can enter a driving transistor because theselecting gate line intersects the driving transistor, are reduced byinputting a signal to a pixel after the selecting gate line thatintersects the driving transistor is no longer selected.

[0111] Given above referring to FIGS. 1 to 4B is a description on anexample of placing a transistor in two pixels. However, the presentinvention is not limited thereto. One transistor may stretch over morethan two pixels.

[0112] An example of extending a transistor over more than two pixels isdescribed with reference to FIG. 5, where one transistor sits on threepixels. In FIG. 5, a transistor length Z504 is three times the pixelpitch N. FIG. 6 is a layout diagram of the pixels of FIG. 5.

[0113] Arrangement of driving transistors shown in FIGS. 5 and 6 makesit possible to design the transistor length arbitrarily. As a result,the number of times a transistor is irradiated with laser light isincreased. With the laser light irradiation number increased,fluctuation in crystal state between channel formation regions isreduced.

[0114] The description given in this embodiment mode is for a case ofdisplaying a color image. However, the present invention is alsoapplicable to monochrome display.

[0115] The description given in this embodiment mode is for a case ofthe stripe arrangement. However, the present invention is not limitedthereto but is applicable to other arrangement such as the deltaarrangement.

[0116] The description given in this embodiment mode is for a case ofconstituting a driving transistor from one transistor. However, pluraltransistors connected in series or parallel may operate as one drivingtransistor. The present invention is also applicable to a transistorarrangement which is suited to plural transistors working as one drivingtransistor.

[0117] The description given in this embodiment mode uses a transistorin which a gate electrode is formed above a channel formation region asshown in FIGS. 4A and 4B, namely, a top gate transistor. However, thepresent invention is also applicable to a bottom gate transistor inwhich a gate electrode is formed below a channel formation region asshown in FIGS. 35A and 35B, and any other transistor structure. This isbecause the present invention does not depend on the structure of atransistor.

[0118] The description given in this embodiment mode is for a pixelcircuit structure in which one pixel has two transistors: a selectingtransistor and a driving transistor. However, the present invention isalso applicable to other circuit structures. Examples thereof includestructures shown in FIGS. 33A and 33B and FIGS. 34A and 34B or in JP2001-343933 A, U.S. Pat. No. 6,229,506 B1, JP 11-219146 A, JP2001-147659 A, etc. In short, the present invention does not depend onthe circuit structure and is applicable to any circuit structure. Amongvarious circuit structures, the present invention is particularlyeffective to a transistor that influences performance of the device anda transistor that is easily affected by fluctuation.

[0119] Other characteristics of the present invention than thosedescribed above are given below. A semiconductor device of the presentinvention has a plurality of transistors arranged to form a matrixpattern, and each transistor has a semiconductor crystallized by laserlight irradiation. Each channel formation region of the pluraltransistors is placed so as to stretch in the first direction. Of theplural transistors, at least two transistors adjacent to each other inthe second direction perpendicular to the first direction have apositional relation that makes them staggered in the second direction.

[0120] The first direction corresponds to the laser scanning direction.Also, the laser scanning direction corresponds to a direction in whichcarriers move in a channel formation region of a transistor when asemiconductor is arranged so as to set the channel length long. In anexample of carrying out the present invention, a semiconductor is placedon two or three pixels as the one in the pixel R(i−1) driving transistor101 of FIG. 1 and the one in the pixel R(i−1) transistor 501 of FIG. 5.This way semiconductors occupy only a small area in a pixel despite thechannel length of each semiconductor of transistors being larger thanthe pixel pitch. The semiconductor shape is not limited to those shownin the above; a semiconductor can take any shape as far as the length ofthe semiconductor is larger than the pixel pitch. The channel length Lor channel width W of a channel formation region may be extended, orboth may be extended at the same time.

[0121] [Embodiment Mode 2]

[0122] This embodiment gives a description with reference to FIGS. 7 to11 on arrangement of driving transistors which is different from that ofEmbodiment Mode 1. FIG. 7 is a schematic diagram of arrangement oftransistors in pixels.

[0123] In FIG. 7, a driving transistor of each pixel is placed so as toreach a region of a surrounding pixel and two transistors are connectedin series or parallel to work as one transistor. Therefore a pixelR(i+1) driving transistor 2704 and a pixel R(i) driving transistor 1701are placed in a pixel R(i). A pixel R(i) driving transistor 2702 isplaced in a pixel R(i−1). The pixel R(i) driving transistor 1701 and thepixel R(i) driving transistor 2702 are electrically connected to eachother. In this manner, a driving transistor of one pixel is placed inthe one pixel and a pixel above in FIG. 7 and the driving transistor inthe one pixel and the driving transistor in the above pixel areelectrically connected to each other.

[0124] The length of a driving transistor therefore corresponds to thesum of the lengths of transistors electrically connected to each other.Accordingly, the length of a driving transistor can be set larger thanthe pixel pitch. This means that, when a transistor is placed inparallel to the laser scanning direction, each transistor is irradiatedwith laser light an increased number of times. Therefore fluctuation incrystal state between semiconductors (channel formation region to beexact) is reduced as well as fluctuation in characteristic amongtransistors.

[0125] Here, as shown in FIG. 30, the laser scan pitch is given as M,the pixel pitch as N, and the transistor length as Z. Then a transistoris irradiated with laser light Z/M times. Since Z>N, Z/M is larger thanN/M (Z/M>N/M).

[0126] The number of times a semiconductor of a transistor is irradiatedwith laser light is thus increased and therefore fluctuation intransistor itself can be reduced. If the transistor length Z issufficiently long, the laser scan pitch M can be set slightly largerthan that in prior art. This makes it possible to reduce the total laserlight irradiation number for irradiating the entire pixel portion.However, in FIG. 1, the transistor length Z starts in one pixel and endsin an adjacent pixel, meaning that the scan pitch M is preferably settwice or less in order to increase the number of times the transistor isirradiated. As a result, processing speed in manufacture of asemiconductor is raised to shorten the manufacture time and manufacturecost is accordingly lowered.

[0127]FIG. 8 is a layout diagram for the pixel in FIG. 7. The pixel R(i)alone is shown as an example in FIG. 8. A circuit diagram for FIG. 8 isFIG. 9. A sectional view of FIG. 8 is FIG. 10B. FIGS. 7 to 9 use thesame symbols for identical components.

[0128] Features of FIG. 8 are as follows.

[0129] The first feature is arrangement of wires that makes a selectinggate line intersect a driving transistor extending over plural pixelsfor electrical connection with the driving transistor. For example, thepixel R(i) driving transistor 1701 climbs over an (i−1)-th row selectinggate line 803 to be electrically connected with the pixel R(i−1) drivingtransistor. Since a transistor intersects and climbs over a selectinggate line that is formed of the layer of a gate wire, a portion of thewire where it is climbed over is formed of the layer of a source wire.This gives a transistor a long channel formation region.

[0130] Another feature is that a driving transistor is arranged inparallel to a power supplying line and a source signal line. Forexample, the pixel R(i) driving transistor 1701 is in parallel to thepower supplying line and the source signal line.

[0131] Therefore a transistor having a long channel formation region canbe placed efficiently.

[0132] By connecting driving transistors in this way, a channelformation region of a driving transistor can have a length larger thanthe pixel pitch. The channel formation length here is the sum of channelformation regions of two transistors since two transistors are connectedin series in this example.

[0133] Described above is an example of placing each transistor in twopixels and connecting one transistor to another. However, the presentinvention is not limited thereto. Each transistor may be extended overmore than two pixels.

[0134] An example of placing a transistor in more than two pixels isshown in FIG. 11, where each transistor is extended over three pixelsand one transistor is connected to another.

[0135] Arrangement of transistors shown in FIG. 11 makes it possible todesign the transistor length arbitrarily. As a result, the number oftimes a transistor is irradiated with laser light is increased. With thelaser light irradiation number increased, fluctuation in crystal statebetween channel formation regions of transistors is reduced andtherefore fluctuation in characteristic among transistors can belowered.

[0136] The description given in this embodiment mode is for a case ofdisplaying a color image. However, the present invention is alsoapplicable to monochrome display.

[0137] The description given in this embodiment mode is for a case ofthe stripe arrangement. However, the present invention is not limitedthereto but is applicable to other arrangement such as the deltaarrangement.

[0138] The description given in this embodiment mode is for a case ofconstituting a driving transistor from one transistor. However, pluraltransistors connected in series or parallel may operate as one drivingtransistor. The present invention is also applicable to a transistorarrangement which is suited to plural transistors working as one drivingtransistor.

[0139] The description given in this embodiment mode uses a transistorin which a gate electrode is formed above a channel formation region asshown in FIGS. 10A and 10B, namely, a top gate transistor. However, thepresent invention is also applicable to a bottom gate transistor inwhich a gate electrode is formed below a channel formation region asshown in FIGS. 35A and 35B, and any other transistor structure. This isbecause the present invention does not depend on the structure of atransistor.

[0140] The description given in this embodiment mode is for a pixelcircuit structure in which one pixel has two transistors: a selectingtransistor and a driving transistor. However, the present invention isalso applicable to other circuit structures. Examples thereof includestructures shown in FIGS. 33A and 33B and FIGS. 34A and 34B or in JP2001-343933 A, U.S. Pat. No. 6,229,506 B1, JP 11-219146 A, JP2001-147659 A, etc. In short, the present invention does not depend onthe circuit structure and is applicable to any circuit structure. Amongvarious circuit structures, the present invention is particularlyeffective to a transistor that influences performance of the device anda transistor that is easily affected by fluctuation.

[0141] Other characteristics of the present invention than thosedescribed above are given below. A semiconductor device of the presentinvention has a plurality of transistors arranged to form a matrixpattern, and each transistor has a semiconductor crystallized by laserlight irradiation. When the semiconductor is irradiated with laserlight, a laser may be moved or the substrate itself may be moved. Eachchannel formation region of the plural transistors is placed so as tostretch in the laser light scanning direction. Of the pluraltransistors, at least two transistors adjacent to each other in thedirection perpendicular to the laser scanning direction have apositional relation that makes them staggered in the laser lightscanning direction.

[0142] Each semiconductor of the plural transistors has a shape obtainedby combining two shapes: a shape axisymmetric to capital letter L and ashape axisymmetric to half-turned capital letter L, and is extended overtwo or three pixels. This way semiconductors occupy only a small area ina pixel despite the channel length of each semiconductor of transistorsbeing larger than the pixel pitch.

[0143] [Embodiment Mode 3]

[0144] The above embodiment modes describe novel arrangement fortransistors. In this embodiment mode, novel arrangement for selectinggate lines will be described with reference to FIGS. 12 to 15B. FIG. 12is a schematic diagram of arrangement of transistors in pixels. FIG. 12shows two pixels arranged in accordance with the stripe arrangement.However, the number of pixels in FIG. 12 will be six if one pixel is tohave one color. For discrimination, the R color portion of the firstpixel from the top of FIG. 12 is referred to as pixel R1, the G colorportion thereof is pixel G1, and the B color portion thereof is pixelB1. Similarly, the R color portion of the second pixel from the top isreferred to as pixel R2, the G color portion thereof is G2, and the Bcolor portion thereof is pixel B2.

[0145] Each pixel has transistors. For instance, the pixel G1 has atransistor for driving a light emitting element of the pixel. Thistransistor is called a pixel G1 driving transistor 1201. Similarly, thepixel G2 has a pixel G2 driving transistor 1202. The same applies to therest of the pixels.

[0146] In the layout diagram of FIG. 12, the pixels are arranged as iftwo pixels form a pair. The driving transistor of the upper pixelextends to a region of the lower pixel whereas the driving transistor ofthe lower pixel extends to a region of the upper pixel. To be specific,the pixel GI driving transistor 1201 extends to a region of the pixel G2whereas the pixel G2 driving transistor 1202 extends to a region of thepixel G1.

[0147] The length of a driving transistor can therefore be set largerthan the pixel pitch. Thus, the laser scanning direction and a directionin which the channel formation region of a transistor stretches can bemade parallel to each other, whereby the number of times each drivingtransistor is irradiated with laser light is increased. Thereforefluctuation in characteristic among transistors is reduced.

[0148] Here, as shown in FIG. 30, the laser scan pitch is given as M,the pixel pitch as N, and the transistor length as Z. Then a transistoris irradiated with laser light Z/M times. Since Z>N, Z/M is larger thanN/M (Z/M>N/M).

[0149] According to the present invention, the number of times atransistor is irradiated with laser light is thus increased andtherefore fluctuation in transistor itself can be reduced. Further, ifthe transistor length Z is sufficiently long, the laser scan pitch M canbe set slightly larger than that in prior art. This makes it possible toreduce the laser light irradiation number for irradiating the entirepixel portion. However, in FIG. 1, the transistor length Z starts in onepixel and ends in an adjacent pixel, meaning that the scan pitch M ispreferably set twice or less in order to increase the number of timesthe transistor is irradiated. As a result, processing speed inmanufacture of a semiconductor device is raised and manufacture cost isaccordingly lowered.

[0150]FIG. 13 is a layout diagram for the pixel in FIG. 12. The pixelsR1, R2, G1, and G2 are shown as an example in FIG. 13. A circuit diagramfor FIG. 13 is FIG. 14. A sectional view of FIG. 13 is FIG. 15B. FIGS.13 to 15B use the same symbols for identical components.

[0151] Features of the Layout Diagram FIG. 13 are as follows.

[0152] The first feature is that, in upper pixels such as the pixel R1and the pixel G1, a selecting gate line and a selecting transistor areplaced on the upper side. For example, an i-th row selecting gate line1303 and a pixel G1 selecting transistor 1301 are placed on the upperside of the pixel. On the other hand, in lower pixels such as the pixelR2 and the pixel G2, a selecting gate line and a selecting transistorare placed on the lower side. For instance, an (i+1)-th row selectinggate line 1305 and a pixel G2 selecting transistor 1306 are placed onthe lower side of the pixel.

[0153] This makes it possible to place a driving transistor of one pixelin another pixel as it is. Specifically, the pixel G1 driving transistor1201 can reach a region of the pixel G2 as it is and the pixel G2driving transistor 1202 can reach a region of the pixel G1 as it is.

[0154] Accordingly, in which part of a pixel region a selecting gateline and a selecting transistor are placed varies from one row toanother. Also, the position of a driving transistor in a pixel region isvaried from one row to another. Furthermore, the position of an ITO filmin a pixel region differs from one row to another. An ITO film forms ananode electrode of a light emitting element and therefore an ITO filmregion (a region inside the ITO film region, to be exact) serves as alight emitting region. Accordingly, the position of a light emittingregion in a pixel region also differs from one row to another.

[0155] Another feature is that a driving transistor, for example, thepixel G1 driving transistor 1201 is arranged in parallel to the powersupplying line and the source signal line. Therefore a long transistorcan be placed efficiently.

[0156] By arranging selecting gate lines in this way, a channelformation region of a driving transistor can have a length larger thanthe pixel pitch.

[0157] The description given in this embodiment mode is for a case ofdisplaying a color image. However, the present invention is alsoapplicable to monochrome display.

[0158] The description given in this embodiment mode is for a case ofthe stripe arrangement. However, the present invention is not limitedthereto but is applicable to other arrangement such as the deltaarrangement.

[0159] The description given in this embodiment mode is for a case ofconstituting a driving transistor from one transistor. However, pluraltransistors connected in series or parallel may operate as one drivingtransistor. The present invention is also applicable to a transistorarrangement which is suited to plural transistors working as one drivingtransistor.

[0160] The description given in this embodiment mode uses a transistorin which a gate electrode is formed above a channel formation region asshown in FIGS. 15A and 15B, namely, a top gate transistor. However, thepresent invention is also applicable to a bottom gate transistor inwhich a gate electrode is formed below a channel formation region asshown in FIGS. 35A and 35B, and any other transistor structure. This isbecause the present invention does not depend on the structure of atransistor.

[0161] The description given in this embodiment mode is for a pixelcircuit structure in which one pixel has two transistors: a selectingtransistor and a driving transistor. However, the present invention isalso applicable to other circuit structures. Examples thereof includestructures shown in FIGS. 33A and 33B and FIGS. 34A and 34B or in JP2001-343933 A, U.S. Pat. No. 6,229,506 B1, JP 11-219146 A, JP2001-147659 A, etc. In short, the present invention does not depend onthe circuit structure and is applicable to any circuit structure. Amongvarious circuit structures, the present invention is particularlyeffective to a transistor that influences performance of the device anda transistor that is easily affected by fluctuation.

[0162] [Embodiment Mode 4]

[0163] In this embodiment mode, a case where driving transistors arearranged in a width direction will be described with reference to FIGS.16 to 18. FIG. 16 is a schematic diagram of arrangement of transistorsin pixels. FIG. 16 shows four pixels arranged in accordance with thestripe arrangement. However, the number of pixels in FIG. 16 will betwelve if one pixel is to have one color. For discrimination, the Rcolor portion of the first pixel from left of FIG. 16 is referred to aspixel R(i), the G color portion thereof is pixel G(i), and the B colorportion thereof is pixel B(i). Similarly, the R color portion of thesecond pixel from left is referred to as pixel R(i+1), the G colorportion thereof is G(i+1), and the B color portion thereof is pixelB(i+1). The R color portion of the third pixel from left is referred toas pixel R(i+2), the G color portion thereof is G(i+2), and the B colorportion thereof is pixel B(i+2). The R color portion of the fourth pixelfrom left is referred to as pixel R(i+3), the G color portion thereof isG(i+3), and the B color portion thereof is pixel B(i+3).

[0164] Each pixel has transistors. For instance, the pixel R(i+1) has atransistor for driving a light emitting element of the pixel. Thistransistor is called a pixel R(i+1) driving transistor 1604. The sameapplies to the rest of the pixels.

[0165] In this embodiment mode, a driving transistor of each pixel isextended in a lateral direction and arranged so as to stretch over aregion of an adjacent pixel as shown in FIG. 16. To be specific, thepixel R(i+1) driving transistor 1604 is extended to a region of thepixels G(i+1), B(i+1), R(i+2), G(i+2), and B(i+2). Thus a drivingtransistor of one pixel is arranged over a region of an adjacent pixel.

[0166] The length of a driving transistor can therefore be set largerthan the pixel pitch. Thus, the laser scanning direction and a directionin which a transistor extends can be made parallel to each other,whereby the number of times each driving transistor is irradiated withlaser light is increased. Therefore fluctuation in characteristic amongtransistors is reduced.

[0167] Here, as shown in FIG. 30, the laser scan pitch is given as M,the pixel pitch as N, and the transistor length as Z. Then a transistoris irradiated with laser light Z/M times. Since Z>N, Z/M is larger thanN/M (Z/M>N/M).

[0168] According to the present invention, the number of times atransistor is irradiated with laser light is thus increased andtherefore fluctuation in transistor itself can be reduced. Further, ifthe transistor length Z is sufficiently long, the laser scan pitch M canbe set slightly larger than that in prior art. This makes it possible toreduce the laser light irradiation number for irradiating the entirepixel portion. However, in FIG. 1, the transistor length Z starts in onepixel and ends in an adjacent pixel, meaning that the scan pitch M ispreferably set twice or less in order to increase the number of timesthe transistor is irradiated. As a result, processing speed inmanufacture of a semiconductor device is raised and manufacture cost isaccordingly lowered.

[0169]FIG. 17 is a layout diagram for the pixel in FIG. 16. The pixelR(i+2) alone is shown as an example in FIG. 17. When layout similar tothis layout is repeated, layout showing the whole pixel portion iscompleted. A circuit diagram for FIG. 17 is FIG. 18. There are used samesymbols for identical components.

[0170] Features of FIG. 17 are as follows.

[0171] The first feature is that a driving transistor is arranged inparallel to a selecting gate line. For example, each driving transistoris placed in parallel to a j-th row selecting gate line 1705. This makesit easy to set the length of a driving transistor long.

[0172] By connecting driving transistors in this way, a drivingtransistor, or in a more accurate term, a channel formation region of adriving transistor can have a length larger than the pixel pitch.

[0173] Described above is an example of placing each transistor in twopixels. However, the present invention is not limited thereto. Eachtransistor may be extended over more than two pixels.

[0174] Such arrangement of transistors makes it possible to design thetransistor length arbitrarily. As a result, it becomes possible toincrease the number of times of laser light irradiation. With the laserlight irradiation number increased, fluctuation in crystal state betweenchannel formation regions of transistors is reduced and thereforefluctuation in characteristic among transistors can be lowered.

[0175] The description given in this embodiment mode is for a case ofdisplaying a color image. However, the present invention is alsoapplicable to monochrome display.

[0176] The description given in this embodiment mode is for a case ofthe stripe arrangement. However, the present invention is not limitedthereto but is applicable to other arrangement such as the deltaarrangement.

[0177] The description given in this embodiment mode is for a case ofconstituting a driving transistor from one transistor. However, pluraltransistors connected in series or parallel may operate as one drivingtransistor. The present invention is also applicable to a transistorarrangement which is suited to plural transistors working as one drivingtransistor.

[0178] The description given in this embodiment mode uses a transistorin which a gate electrode is formed above a channel formation region asshown in FIGS. 4A and 4B, namely, a top gate transistor. However, thepresent invention is also applicable to a bottom gate transistor inwhich a gate electrode is formed below a channel formation region asshown in FIGS. 35A and 35B, and any other transistor structure. This isbecause the present invention does not depend on the structure of atransistor.

[0179] The description given in this embodiment mode is for a pixelcircuit structure in which one pixel has two transistors: a selectingtransistor and a driving transistor. However, the present invention isalso applicable to other circuit structures. Examples thereof includestructures shown in FIGS. 33A and 33B and FIGS. 34A and 34B or in JP2001-343933 A, U.S. Pat. No. 6,229,506 B1, JP 11-219146 A, JP2001-147659 A, etc. In short, the present invention does not depend onthe circuit structure and is applicable to any circuit structure. Amongvarious circuit structures, the present invention is particularlyeffective to a transistor that influences performance of the device anda transistor that is easily affected by fluctuation.

[0180] [Embodiment Mode 5]

[0181] In this embodiment mode, novel arrangement for pixels will bedescribed with reference to FIGS. 19 to 22. The pixels are arranged inthe lateral direction in order of red, green, and blue in accordancewith the normal stripe arrangement. FIG. 19 is a schematic diagram ofarrangement of transistors in pixels when the pixels are arrangedlongitudinal direction in order of red, green, and blue. FIG. 19 showsfour pixels arranged longitudinal direction in order of red, green, andblue in accordance with the stripe arrangement. However, the number ofpixels in FIG. 19 will be twelve if one pixel is to have one color. Fordiscrimination, the R color portion of the first pixel from left of FIG.19 is referred to as pixel R(i−1), the G color portion thereof is pixelG(i−1), and the B color portion thereof is pixel B(i−1). Similarly, theR color portion of the second pixel from left is referred to as pixelR(i), the G color portion thereof is G(i), and the B color portionthereof is pixel B(i). The R color portion of the third pixel from leftis referred to as pixel R(i+1), the G color portion thereof is G(i+1),and the B color portion thereof is pixel B(i+1). The R color portion ofthe fourth pixel from left is referred to as pixel R(i+2), the G colorportion thereof is G(i+2), and the B color portion thereof is pixelB(i+2).

[0182] Each pixel has transistors. For instance, the pixel R(i−1) has atransistor for driving a light emitting element of the pixel. Thistransistor is called a pixel R(i−1) driving transistor 1901. The sameapplies to the rest of the pixels.

[0183] In this embodiment mode, a driving transistor of each pixel isextended lateral direction and arranged over a region of an adjacentpixel as shown in FIG. 19. To be specific, the pixel R(i−1) drivingtransistor 1901 is extended to a region of the pixel R(i). Similarly,the pixel R(i) driving transistor 1902 is extended to a region of thepixel R(i+1). Thus a driving transistor of one pixel is placed not onlyon the one pixel but also on a region of an adjacent pixel.

[0184] Here, as shown in FIG. 30, the laser scan pitch is given as M,the pixel pitch as N, and the transistor length as Z. Then a transistoris irradiated with laser light Z/M times. Since Z>N, Z/M is larger thanN/M (Z/M>N/M).

[0185] The number of times of laser light irradiation is thus increasedand therefore fluctuation in transistor itself can be reduced.Conversely, if the transistor length Z is sufficiently long, the laserscan pitch M can be set slightly larger than that in prior art. Thismakes it possible to reduce the laser light irradiation number forirradiating the entire pixel portion. However, in FIG. 1, the transistorlength Z starts in one pixel and ends in an adjacent pixel, meaning thatthe scan pitch M is preferably set twice or less in order to increasethe number of times the transistor is irradiated. As a result,processing speed in manufacture of a semiconductor is raised andmanufacture cost is accordingly lowered.

[0186]FIG. 19 is a layout diagram for the pixel in FIG. 20. The pixelR(i) is shown as an example in FIG. 20. A circuit diagram for FIG. 20 isFIG. 21. FIGS. 19 to 21 use the same symbols for identical components.

[0187] Features of FIG. 20 are as follows.

[0188] The first feature is that a driving transistor is arranged inparallel to a selecting gate line. For example, each driving transistoris placed in parallel to a j-th row selecting gate line 2001. This makesit easy to set the length of a driving transistor long.

[0189] Colors of the pixels are arranged longitudinal direction in orderof red, green, and blue. As a result, when the driving transistors arearranged lateral direction, it becomes easy to set the length of adriving transistor long.

[0190] By connecting driving transistors in this way, a drivingtransistor, or in a more accurate term, a channel formation region of adriving transistor can have a length larger than the pixel pitch.

[0191] Described above is an example of placing each transistor in twopixels. However, the present invention is not limited thereto. Eachtransistor may be extended over more than two pixels.

[0192] An example of placing a transistor in more than two pixels isshown in FIG. 22, where each transistor is extended over three pixels.

[0193] Arrangement of transistors shown in FIG. 22 makes it possible todesign the transistor length arbitrarily. As a result, the number oftimes of laser light irradiation is increased. With the laser lightirradiation number increased, fluctuation in crystal state betweenchannel formation regions of transistors is reduced and thereforefluctuation in characteristic among transistors can be lowered.

[0194] The description given in this embodiment mode is for a case ofdisplaying a color image. However, the present invention is alsoapplicable to monochrome display.

[0195] The description given in this embodiment mode is for a case ofthe stripe arrangement. The present invention is not limited thereto butis applicable to other arrangement such as the delta arrangement.

[0196] The description given in this embodiment mode is for a case ofconstituting a driving transistor from one transistor. However, pluraltransistors connected in series or parallel may operate as one drivingtransistor. The present invention is also applicable to a transistorarrangement which is suited to plural transistors working as one drivingtransistor.

[0197] The description given in this embodiment mode uses a transistorin which a gate electrode is formed above a channel formation region asshown in FIGS. 15A and 15B, namely, a top gate transistor. However, thepresent invention is also applicable to a bottom gate transistor inwhich a gate electrode is formed below a channel formation region asshown in FIGS. 35A and 35B, and any other transistor structure. This isbecause the present invention does not depend on the structure of atransistor.

[0198] The description given in this embodiment mode is for a pixelcircuit structure in which one pixel has two transistors: a selectingtransistor and a driving transistor. However, the present invention isalso applicable to other circuit structures. Examples thereof includestructures shown in FIGS. 33A and 33B and FIGS. 34A and 34B or in JP2001-343933 A, U.S. Pat. No. 6,229,506 B1, JP 11-219146 A, JP2001-147659 A, etc. In short, the present invention does not depend onthe circuit structure and is applicable to any circuit structure. Amongvarious circuit structures, the present invention is particularlyeffective to a transistor that influences performance of the device anda transistor that is easily affected by fluctuation.

[0199] Other characteristics of the present invention than thosedescribed above are given below. A semiconductor device of the presentinvention has a plurality of transistors arranged to form a matrixpattern, and each transistor has a semiconductor crystallized by laserlight irradiation. Each channel formation region of the pluraltransistors is placed so as to stretch in the first direction. Of theplural transistors, at least two transistors adjacent to each other inthe second direction perpendicular to the first direction have apositional relation that makes them staggered in the second direction.

[0200] The first direction corresponds to the laser scanning direction.Also, the laser scanning direction corresponds to a direction in whichcarriers move in a channel formation region of a transistor when asemiconductor is arranged so as to set the channel length long. In anexample of carrying out the present invention, a semiconductor is placedon two or three pixels as the one in the pixel R(i−1) driving transistor101 of FIG. 1 and the one in the pixel R(i−1) transistor 501 of FIG. 5.This way semiconductors occupy only a small area in a pixel despite thechannel length of each semiconductor of transistors being larger thanthe pixel pitch. The semiconductor shape is not limited to those shownin the above; a semiconductor can take any shape as far as the length ofthe semiconductor is larger than the pixel pitch. The channel length Lor channel width W of a channel formation region is extended, or bothare extended at the same time.

[0201] [Embodiment 1]

[0202] The cross-sectional view in this specification has showed only upto an ITO layer. Next, a cross-sectional view that includes lightemitting element is shown. In FIG. 23, a cross-sectional view shows thatlight is emitted toward a bottom, that is, a glass. In FIG. 24, across-sectional view shows that light is emitted toward a top.

[0203] In FIG. 23, a light emitting layer 2301 is laminated on an ITO,and a cathode 2302 is laminated thereon. Materials that are made usingknown technique are laminated to form the structure of light emittinglayer 2301.

[0204] As an example of the light emitting layer 2301, there is a layerin which a hole injection layer, a hole transporting layer, a lightemitting layer, an electron transporting layer, and an electroninjection layer are laminated is widely used.

[0205] In FIG. 24, a light emitting layer 2401 is laminated on an anodewiring. A cathode which is transparent to light, that is, a transparentcathode 2402 is formed thereon, however, an anode can be replaced by thecathode.

[0206] This cross-sectional structure can be formed using knowntechnique. This embodiment can be used for above-mentioned EmbodimentModes 1 to 5. Therefore, a semiconductor device of the present inventioncan display an image.

[0207] [Embodiment 2]

[0208] A light emitting device using a light emitting element as a lightemitting display is a self light emission type. Thus, such a lightemitting device has high visibility in a light place and a wide viewingangle, as compared with a liquid crystal display. Therefore, it can beused for a display portion of various electronic devices.

[0209] As electronic devices using a light emitting display of thepresent invention, there are a video camera, a digital camera, a goggletype display (head mount display), a navigation system, a soundreproducing device (car audio system, audio component system, or thelike), a laptop personal computer, a game machine, a portableinformation terminal (mobile computer, mobile telephone, portable gamemachine, an electric book, or the like), an image reproducing deviceincluding a recording medium (specifically, apparatus for reproducing animage from a recording medium such as a digital versatile disc (DVD),which includes a display capable of displaying the image), and the like.In particular, in the case of the portable information terminal in whicha screen is viewed from an oblique direction in many cases, it isimportant that a view angle is large. Thus, it is desirable that thelight emitting device is used. Concrete examples of those electronicdevices are shown in FIGS. 25A to 25H.

[0210]FIG. 25A shows a display device which includes a cabinet 3001, asupport base 3002, a display portion 3003, a speaker portion 3004, and avideo input terminal 3005. The light emitting display of the presentinvention can be used for the display portion 3003. The light emittingdevice is a self light emission type and thus does not require a backlight. Therefore, a thinner display portion than a liquid crystaldisplay can be obtained. Further, the display device includes alldisplay devices for information display such as personal computer, TVbroadcast receiving, and advertisement display.

[0211]FIG. 25B is a digital still camera, which is composed of a mainbody 3101, a display portion 3102, an image-receiving portion 3103,operation keys 3104, external connection ports 3105, a shutter 3106, andthe like. The semiconductor device of the present invention can be usedin the display portion 3102.

[0212]FIG. 25C is a notebook personal computer, which is composed of amain body 3201, a frame 3202, a display portion 3203, a keyboard 3204,external connection ports 3205, a pointing mouse 3206, and the like. Thesemiconductor device of the present invention can be used in the displayportion 3203.

[0213]FIG. 25D is a mobile computer, which is composed of a main body3301, a display portion 3302, a switch 3303, operation keys 3304, aninfrared port 3305, and the like. The semiconductor device of thepresent invention can be used in the display portion 3302.

[0214]FIG. 25E is a portable image reproducing device equipped with arecording medium (specifically, a DVD player), and is composed of a mainbody 3401, a frame 3402, a display portion A 3403, a display portion B3404, a recording medium (such as a DVD) read-in portion 3405, operationkeys 3406, a speaker portion 3407, and the like. The display portion A3403 mainly displays image information, and the display portion B 3404mainly displays character information, and the semiconductor device ofthe present invention can be used in the display portion A 3403 and inthe display portion B 3404. Note that family game machines and the likeare included in the category of image reproducing devices provided witha recording medium.

[0215]FIG. 25F is a goggle type display device (head mounted display),which is composed of a main body 3501, a display portion 3502, and anarm portion 3503. The semiconductor device of the present invention canbe used in the display portion 3502.

[0216]FIG. 25G is a video camera, which is composed of a main body 3601,a display portion 3602, a frame 3603, external connection ports 3604, aremote control receiving portion 3605, an image receiving portion 3606,a battery 3607, an audio input portion 3608, operation keys 3609, andthe like. The semiconductor device of the present invention can be usedin the display portion 3602.

[0217]FIG. 25H is a mobile telephone, which is composed of a main body3701, a frame 3702, a display portion 3703, an audio input portion 3704,an audio output portion 3705, operation keys 3706, external connectionports 3707, an antenna 3708, and the like. The semiconductor device ofthe present invention can be used in the display portion 3703. Note thatwhite characters are displayed on a black background in the displayportion 3703, and thus, the power consumption of the mobile telephonecan be suppressed.

[0218] Note that, when a light emitting intensity of an organic lightemitting material is increased in future, it can be used for a fronttype or a rear type projector for magnifying and projecting outputtedlight including image information by a lens or the like.

[0219] Also, in the above electronic devices, the number of cases whereinformation distributed through an electronic communication line such asan Internet or a CATV (cable television) is displayed is increased. Inparticular, an opportunity in which moving image information isdisplayed is increased. A response speed of the organic light emittingmaterial is very high. Thus, the light emitting device is preferable formoving image display.

[0220] Also, with respect to the light emitting device, power isconsumed in a portion which emits light. Thus, it is desirable thatinformation is displayed so as to minimize an area of a light emittingportion. Accordingly, when the light emitting device is used for adisplay portion of, a portable information terminal, particularly, amobile telephone or a sound reproducing device in which characterinformation is mainly displayed, it is desirable that the light emittingdevice is driven so as to use a non-light emitting portion as abackground and produce character information in a light emittingportion.

[0221] As described above, an application area of the present inventionis extremely wide and can be used for electronic devices in all fields.

[0222] In the present invention, a plurality of transistors are arrangedto form a matrix pattern, and each transistor has a semiconductorcrystallized by laser light irradiation. Each channel formation regionof the plural transistors is placed so as to stretch in a firstdirection (the laser scanning direction). Of the plural transistors, atleast two transistors adjacent to each other in a second direction thatis perpendicular to the first direction have a positional relation thatmakes them staggered in the second direction. Each semiconductor of theplural transistors has a shape obtained by combining two shapes: a shapeaxisymmetric to capital letter L and a shape axisymmetric to half-turnedcapital letter L, and is extended over two pixels. This waysemiconductors occupy only a small area in a pixel despite the channellength of each semiconductor of transistors being larger than the pixelpitch.

[0223] In the present invention, semiconductors are placed in parallelto Direction x (the laser light scanning direction) to even outfluctuation in characteristic between a transistor in one point inDirection x (the laser light scanning direction) and a transistor inanother point. By arranging transistors in parallel to Direction x (thelaser light scanning direction), channel formation regions of thetransistors are irradiated with a laser in an increased number of times.This reduces fluctuation in crystal state between channel formationregions in transistors, whereby fluctuation in characteristic among thetransistors is lowered.

[0224] Furthermore, in the present invention, each semiconductor isarranged so as to stretch over at least two pixels in order to increasethe number of times the semiconductor is irradiated with a laser. Thismakes the length of the semiconductor larger than the pixel pitch of thepixels. By thus increasing the transistor size and setting a channellength L larger than the channel width, fluctuation in transistor itselfcan be reduced.

[0225] If the pixel pitch is increased in future, the semiconductorlength can be set even longer and therefore the laser light irradiationnumber is further increased. As a result, fluctuation among transistorsthat have those semiconductors is reduced and the present invention willhave even greater effects.

[0226] The width and length of laser light and the laser scan pitch inirradiating the semiconductors are not particularly limited. However,since the semiconductors are irradiated with laser light an increasednumber of times in the present invention, widening the laser light andmeasures to the similar effect are preferable. This makes it possible tofurther reduce fluctuation in crystal state between channel formationregions of the transistors and therefore fluctuation in characteristicamong the transistors can be reduced even more. If each semiconductor issufficiently long, the laser light irradiation number for eachsemiconductor can be satisfactorily large and fluctuation amongtransistors is reduced even when the laser scan pitch is somewhatlarger. In this way, a semiconductor device is manufactured withoutincreasing the total number of laser light irradiation for irradiatingthe entire pixel portion. As a result, processing speed in manufactureof a semiconductor device is raised and therefore the cost is lowered.

What is claimed is:
 1. A semiconductor device comprising a plurality oftransistors which form a matrix pattern, comprising: wherein theplurality of transistors have semiconductor films crystallized by alaser light irradiation, wherein each channel formation region of theplurality of transistors is placed so as to extend in a first direction,and wherein, in the plurality of transistors, at least two transistorswhich are adjacent to each other in a second direction that isperpendicular to the first direction have a positional relation thatmakes them staggered in the second direction.
 2. A semiconductor deviceaccording to claim 1, wherein the first direction is a direction inwhich electric charges move in the channel formation regions of thetransistors.
 3. A semiconductor device according to claim 1, wherein adirection in which electric charges move in the channel formationregions of the plurality of transistors is parallel to a scanningdirection of the laser light.
 4. A semiconductor device according toclaim 1, wherein the semiconductor device is at least one selected fromthe group consisting of a digital camera, a personal computer, a mobilecomputer, an image reproducing device, a goggle type display, a videocamera, and a mobile telephone.
 5. A semiconductor device comprising aplurality of transistors which form a matrix pattern, wherein theplurality of transistors have semiconductor films crystallized by alaser light irradiation, wherein each channel formation region of theplurality of transistors is placed so as to extend in a first direction,wherein, of the plurality of transistors, at least two transistors whichare adjacent to each other in a second direction that is perpendicularto the first direction have a positional relation that makes themstaggered in the second direction, and wherein, in the semiconductorfilms of the plurality of transistors, at least two semiconductor filmswhich are adjacent to each other in the second direction have a samecrystal state.
 6. A semiconductor device according to claim 5, whereinthe first direction is a direction in which electric charges move in thechannel formation regions of the transistors.
 7. A semiconductor deviceaccording to claim 5, wherein a direction in which electric charges movein the channel formation regions of the plurality of transistors isparallel to a scanning direction of the laser light.
 8. A semiconductordevice according to claim 5, wherein the semiconductor device is atleast one selected from the group consisting of a digital camera, apersonal computer, a mobile computer, an image reproducing device, agoggle type display, a video camera, and a mobile telephone.
 9. Asemiconductor device comprising a plurality of pixels having transistorsforming a matrix pattern, wherein the transistors have semiconductorfilms crystallized by a laser light irradiation, wherein thesemiconductor films extend over at least two pixels, wherein a length ofeach of the semiconductor films is longer than a pixel pitch of thepixels, and wherein, when a scan pitch of the laser light is given as Mand the pixel pitch of the pixels is given as N, each of thesemiconductor films is irradiated with the laser light N/M times ormore.
 10. A semiconductor device according to claim 9, wherein adirection in which electric charges move in the channel formationregions of the plurality of transistors is parallel to a scanningdirection of the laser light.
 11. A semiconductor device according toclaim 9, wherein the semiconductor device is at least one selected fromthe group consisting of a digital camera, a personal computer, a mobilecomputer, an image reproducing device, a goggle type display, a videocamera, and a mobile telephone.
 12. A semiconductor device having aplurality of pixels and wires, the pixels having transistors, the pixelsand the wires forming a matrix pattern, wherein the transistors havesemiconductor films crystallized by a laser light irradiation, whereineach of the semiconductor films extends in parallel to the wires andextending over at least two pixels, wherein a length of each of thesemiconductor films is longer than a pixel pitch of the pixels, andwherein, when a scan pitch of the laser light is given as M and thepixel pitch of the pixels is given as N, each of the semiconductor filmsis irradiated with the laser light N/M times or more.
 13. Asemiconductor device according to claim 12, wherein a direction in whichelectric charges move in the channel formation regions of the pluralityof transistors is parallel to a scanning direction of the laser light.14. A semiconductor device according to claim 12, wherein thesemiconductor device is at least one selected from the group consistingof a digital camera, a personal computer, a mobile computer, an imagereproducing device, a goggle type display, a video camera, and a mobiletelephone.
 15. A semiconductor device comprising: a first transistorhaving at least a first channel region; and a second transistor havingat least a second channel region, wherein the first channel region andthe second channel region are adjacent to each other, and wherein thefirst channel region and the second channel region extend in onedirection, and partially overlap with each other.
 16. A semiconductordevice according to claim 15, wherein the first direction is a directionin which electric charges move in the channel formation regions of thetransistors.
 17. A semiconductor device according to claim 15, whereinthe semiconductor device is at least one selected from the groupconsisting of a digital camera, a personal computer, a mobile computer,an image reproducing device, a goggle type display, a video camera, anda mobile telephone.
 18. A semiconductor device comprising: a firsttransistor having at least a first channel region; and a secondtransistor having at least a second channel region, wherein the firstchannel region and the second channel region are adjacent to each other,wherein the first channel region and the second channel region extend inone direction, and partially overlap with each other, and wherein thefirst channel region and the second channel region have a same crystalstate.
 19. A semiconductor device according to claim 18, wherein thefirst direction is a direction in which electric charges move in thechannel formation regions of the transistors.
 20. A semiconductor deviceaccording to claim 18, wherein the semiconductor device is at least oneselected from the group consisting of a digital camera, a personalcomputer, a mobile computer, an image reproducing device, a goggle typedisplay, a video camera, and a mobile telephone.
 21. A method ofmanufacturing a semiconductor device, comprising: irradiating asemiconductor film with a laser light; and forming a plurality oftransistors from the crystallized semiconductor film and arranging theplurality of transistors into a matrix pattern, wherein each channelformation region of the plurality of transistors is placed so as toextend in a first direction, and wherein, in the plurality oftransistors, at least two transistors which are adjacent to each otherin a second direction that is perpendicular to the first direction havea positional relation that makes them staggered in the second direction.22. A method of manufacturing a semiconductor device according to claim21, wherein the first direction is a direction in which electric chargesmove in the channel formation regions of the transistors.
 23. A methodof manufacturing a semiconductor device according to claim 21, wherein adirection in which electric charges move in the channel formationregions of the plurality of transistors is parallel to a scanningdirection of the laser light.
 24. A method of manufacturing asemiconductor device according to claim 21, wherein the semiconductordevice is at least one selected from the group consisting of a digitalcamera, a personal computer, a mobile computer, an image reproducingdevice, a goggle type display, a video camera, and a mobile telephone.25. A method of manufacturing a semiconductor device, comprising:irradiating a semiconductor film with a laser light; and forming aplurality of transistors from the crystallized semiconductor film andarranging the plurality of transistors into a matrix pattern, whereineach channel formation region of the plurality of transistors is placedso as to extend in a first direction, wherein, of the plurality oftransistors, at least two transistors which are adjacent to each otherin a second direction that is perpendicular to the first direction havea positional relation that makes them staggered in the second direction,and wherein, in the plurality of semiconductor films of the plurality oftransistors, at least two semiconductor films which are adjacent to eachother in the second direction have a same crystal state.
 26. A method ofmanufacturing a semiconductor device according to claim 25, wherein thefirst direction is a direction in which electric charges move in thechannel formation regions of the transistors.
 27. A method ofmanufacturing a semiconductor device according to claim 25, wherein adirection in which electric charges move in the channel formationregions of the plurality of transistors is parallel to a scanningdirection of the laser light.
 28. A method of manufacturing asemiconductor device according to claim 25, wherein the semiconductordevice is at least one selected from the group consisting of a digitalcamera, a personal computer, a mobile computer, an image reproducingdevice, a goggle type display, a video camera, and a mobile telephone.29. A method of manufacturing a semiconductor device, comprising:irradiating a semiconductor film with a laser light; and forming aplurality of transistors from the crystallized semiconductor film byetching the crystallized semiconductor film into a plurality ofsemiconductor layers, wherein the plurality of semiconductor layersextend over at least two pixels; wherein a length of each of theplurality of semiconductor layers is longer than a pixel pitch of thepixels, and wherein, when a scan pitch of the laser light is given as Mand the pixel pitch of the pixels is given as N, each of the pluralityof semiconductor layers is irradiated with the laser light N/M times ormore.
 30. A method of manufacturing a semiconductor device according toclaim 29, wherein a direction in which electric charges move in thechannel formation regions of the plurality of transistors is parallel toa scanning direction of the laser light.
 31. A method of manufacturing asemiconductor device according to claim 29, wherein the semiconductordevice is at least one selected from the group consisting of a digitalcamera, a personal computer, a mobile computer, an image reproducingdevice, a goggle type display, a video camera, and a mobile telephone.32. A method of manufacturing a semiconductor device, comprising:irradiating a semiconductor film with a laser light; and formingtransistors from the crystallized semiconductor film by etching thecrystallized semiconductor film into a plurality of semiconductorlayers, wherein each of the plurality of semiconductor layers extends inparallel to wires and extends over at least two pixels, wherein a lengthof each of the semiconductor layers is longer than a pixel pitch of thepixels, and wherein, when a scan pitch of the laser light is given as Mand the pixel pitch of the pixels is given as N, each of the pluralityof semiconductor layers is irradiated with the laser light N/M times ormore.
 33. A method of manufacturing a semiconductor device according toclaim 32, wherein a direction in which electric charges move in thechannel formation regions of the plurality of transistors is parallel toa scanning direction of the laser light.
 34. A method of manufacturing asemiconductor device according to claim 32, wherein the semiconductordevice is at least one selected from the group consisting of a digitalcamera, a personal computer, a mobile computer, an image reproducingdevice, a goggle type display, a video camera, and a mobile telephone.